1. TECHNICAL FIELD OF THE INVENTION
This invention relates to a device for selectively charging an analysing apparatus with liquid or gaseous sample, reference or cleansing media, comprising a sample inlet opening and a feeder unit with fittings for the media to be introduced.
2. DISCUSSION OF THE RELATED ART
Chemical analyses utilizing the kind of test equipment for which the above feeding device is designed, are preferably performed by introducing the sample via the above sample feeding device into the respective measuring chamber, where it is brought into contact with measuring sensors. As a result of the interaction between the sample and these sensors an electric signal will eventually be generated, in general by means of physical or chemical interactions, which is functionally dependent on the concentration of the substance to be determined in the sample.
Devices of this type are known, for instance for carrying out blood gas analyses or electrolyte analyses with the use of electrochemical or optochemical sensors. Examples of the substance concentrations measured include the pH value of a blood sample, the partial pressure of oxygen in molecular solution, the partial pressure of CO.sub.2 in molecular solution, and, possibly, a number of ions, enzymes and non-electrolytes contained in the solution, such as glucose, etc.--parameters which in their entirety provide information on the state of the sample and, as such, on the constitution of the test person.
The analysing apparatus should therefore be provided with a device permitting the feeding of all kinds of sample materials into the measuring chambers, and it should also be possible to introduce calibrating liquids, calibrating gases, cleansing solutions, test solutions, i.e. media of a liquid or gaseous type, in a simple manner, with the samples being fed into the inlet opening from their conventional sample containers, such as syringes or capillary glass tubes. Depending on the desired or specified method of operation and optimised sample manipulation, the sample is injected into the inlet opening from a syringe, or it is forced in from capillary tubes of variable length and diameter by means of a pumping device of the analysing apparatus. If gaseous samples or calibrating media are to be introduced, great care should be taken to avoid the build-up of dynamic pressure anywhere in the sample path, since this might falsify the absolute value of the respective partial pressure of the gas.
A device of the above type, for example for feeding selected media into an electrochemical test apparatus, is described in EP-A-O 112 324. This device is provided with a feeder unit carrying fittings for introducing calibrating and reference media, and a sealed piece of pipe positioned in a bore, which is movable relative to the feeder unit. On its end facing away from the measuring chamber this piece of pipe has a fitting for the sample, as well as one or more bores along its circumference, which may be aligned with at least one of the above fittings for the calibrating and reference media by means of a relative motion between the piece of pipe and the feeder unit, which is controlled by a stepping motor.
Although this device has proved successful, it suffers from the drawback that the paths to the measuring chamber travelled by the sample medium and any reference or calibrating media will differ, even if only slightly, where interactions with the materials of the paths and differences in temperature and pressure may occur. This means that sample, reference and calibrating media are not subject to identical conditions, which may result in considerable errors of measurement.
It is an object of the present invention to avoid the disadvantages of previous devices and to propose a feeding device offering identical measuring conditions for all media to be introduced.